Metal nitride layers have been used in the fabrication of semiconductor devices. In particular, metal nitride layers have been used to form not only the upper and lower electrodes of capacitors in volatile semiconductor memory devices, but also as gate electrodes for volatile and nonvolatile semiconductor memory devices. Further, metal nitride layers have also been used to conformally fill contact holes in a metallization process in order to decrease the contact resistance between upper and lower conductive elements in multi-layered semiconductor electronic structures.
However, when a metal nitride layer is formed on a semiconductor substrate, projections may be formed at the surface of the metal nitride layer due to the presence of chlorine (Cl) in the layer. In cases where the metal nitride layer is used as the material of the upper and/or lower electrodes of a capacitor, such projections can increase leakage current during operation of the device. Further, in cases where the metal nitride layer is used as the gate electrode of an electronic device, such projections can cause an electrical short between the gate electrode pattern and a peripheral circuit wire. Moreover, in cases where the metal nitride layer is used in a contact hole, such projections may prevent an upper conductive element from making good contact with the metal nitride material, thereby increasing the contact resistance between upper and lower conductive regions in the structure. Accordingly, it may be desirable to reduce or eliminate the chlorine projections from metal nitride layers formed during semiconductor fabrication processes.
U.S. Pat. No. 6,548,402 to Wang, et al. discloses a method of depositing a thick titanium nitride film using a reaction between ammonia (NH3) and titanium tetrachloride (TiCl4). In one embodiment, an NH3:TiCl4 ratio of about 8.5 is used to deposit a TiN layer at a temperature of about 500° C. at a pressure of about 20 torr. In another embodiment, a composite TiN layer is formed by alternately depositing TiN layers of different thicknesses, using process conditions having different NH3:TiCl4 ratios. In one preferred embodiment, a TiN layer of less than about 20 Å is formed at an NH3:TiCl4 ratio of about 85, followed by a deposition of a thicker TiN layer at an NH3:TiCl4 ratio of about 8.5. By repeating the alternate film deposition using the two different process conditions, a composite TiN layer is formed.